The present invention relates to generally techniques for performing orientation (more specifically, azimuth) measuring calibration (offset correction) on the basis of orientation measuring data using a geomagnetic sensor. More particularly, the present invention relates to an improved orientation data generation method, orientation sensor unit and portable electronic equipment which, even when data obtained from a three-axis geomagnetic sensor are limited within a particular plane, can perform appropriate calibration to measure a correct orientation (or azimuth).
Portable terminals, such as portable phones, are known, which include a magnetic sensor for detecting geomagnetism and measure orientations on the basis of the geomagnetism detected by the magnetic sensor. The orientations measured in this manner are used, for example, to display a map. Recently, there have appeared portable terminals which are, for example, equipped with a GPS (Global Positioning System) function for detecting a position and has a function for displaying a map based on a current position in accordance with a current orientation (or azimuth) of the portable terminal.
However, in the portable terminals, there exists magnetism leaking from a speaker and microphone provided on the terminal, metal packages of magnetized electronic components, etc. Thus, the magnetic sensors provided in the portable terminals would detect a magnetic filed that comprises a combination of magnetic fields produced from the electronic components etc. within the terminal and the geomagnetism or earth's magnetism. For this reason, a calibration process has to be performed to compensate for error (offsets) caused due to the magnetic fields produced from the electronic components etc. within the terminal. Therefore, in order to perform the calibration process in the conventional portable terminals provided with a two-axis magnetic sensor, it has been conventional for the user to, for example, rotate or turn the portable terminal through 180 degrees so that the portable terminal can gather measured data from the magnetic sensor during the turning movement and estimate offsets on the basis of the measured data.
Among various conventionally-known techniques pertaining to calibration of a magnetic sensor provided in a portable terminal is one disclosed in Japanese Patent Application Laid-open Publication No. 2004-12416. According to the disclosed technique, the portable terminal is turned stepwise, a predetermined angle at a time, and offsets are estimated on the basis of data measured by the magnetic sensor at each of the angles, so that the calibration is performed without depending on the turning speed.
However, even with the technique disclosed in the No. 2004-12416 publication, the user must bother to turn the portable equipment, provided with the magnetic sensor, to perform the calibration process. Namely, although the disclosed technique can achieve some improvement over the traditional techniques, it necessitates the user to perform particular calibrating operation, so that the calibration in the disclosed technique is still as cumbersome to the user as in the traditional techniques. Particularly, where the magnetic sensor is a three-axis geomagnetic sensor, the user has to perform even more cumbersome operation because data of the three axes are required.
In order to perform accurate calibration in the case where the magnetic sensor is a three-axis geomagnetic sensor, it is preferable that data acquired via the geomagnetic sensor lie uniformly within a compass sphere (or orientation sphere); if the acquired data concentrate (i.e., are limited) within a particular plane, the calibration can not be performed in a satisfactory manner.